The Associated Press’ Twitter account posted this message on Tuesday afternoon: “Breaking: Two Explosions in the White House and Barack Obama is injured.”

The message was fake, the account was quickly suspended, and the news organization quickly announced through other channels that it had been hacked — but not before some damage was done.

The Dow Jones Industrial Average immediately plunged roughly 150 points, The Washington Post said. It recovered, but in just a couple minutes $136 billion had been wiped out.

That is a big risk of computerized trading, Bloomberg says: Humans know better, but computers don’t. Algorithms reading headlines can mess up trades faster than people can notice nothing is actually wrong and intervene.

There are some safeguards — for instance, individual stocks weren’t hurt because most companies’ shares briefly halt trading if there’s a sudden 10 percent dip in value. But the exchanges don’t want to talk about the problem. Representatives for Nasdaq, NYSE Euronext, and CME Group all declined to comment to Bloomberg.

A group of Syrian hackers who support President Bashar al-Assad claimed responsibility for the attack, but offered no proof. They supposedly used a phishing email to trick an AP staffer into giving access to the account, which has more than 1 million followers.

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